Morphological and microstructural stability of boron-doped diamond thin film electrodes in an acidic chloride medium at high anodic current densities

Boron-doped diamond thin films have been examined before and after high-current-density electrolysis to investigate the morphological and microstructural stability of this new electrode material. The diamond thin films were used to generate chlorine from a solution of 1.0 M HNO3 + 2.0 M NaCl at current densities of 0.05 and 0.5 A/cm(2) for times up to 20 h. Comparative studies were made using common ''graphitic'' electrodes including highly oriented pyrolytic graphite, glassy carbon, and Grafoil (R). The electrodes were characterized using four-point probe resistivity measurements, atomic force microscopy, scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and cyclic voltammetry. In all cases, no severe morphological or microstructural damage (i.e., corrosion) was observed on films exposed to the highest current density. There were surface compositional changes in the forms of oxygenation and nondiamond carbon impurity etching that produced an increase in the reaction overpotential. Specifically, the overpotential was supposed to result from a combination of decreased surface conductivity due to the formation of carbon-oxygen functional groups and loss of kinetically active redox sites due to the oxidative etching of nondiamond carbon impurities.